You will need to install a user script manager extension to install this script.
This script should not be not be installed directly. It is a library for other scripts to include with the meta directive
// @require https://update.sleazyfork.org/scripts/420841/1208330/Image%20Board%20Enhancer%20Icons.js
Icons for Image Board Enhancer https://greasyfork.org/en/scripts/387312-image-board-enhancer-rule34-gelbooru-e621-and-more